LEOPOLD I. (164o-1705), Roman emperor, second son of the emperor Ferdinand III. and his first wife Maria Anna, daugh ter of Philip III. of Spain, was born on June 9, 1640. Leopold was intended for the church, but the death of his elder brother, the German king Ferdinand IV., in July 1654, made him his father's heir. In 1655 he was chosen king of Hungary and in 1656 king of Bohemia, and in July 1658, more than a year after his father's death, he was elected emperor at Frankfort. For nearly the whole 47 years of his reign Leopold was pitted against Louis XIV. of France. The emperor was a man of peace, and never directed his armies in person, but the empire was at war for the greater part of his reign. (See EUROPE : History.) He was the ally of Poland against Charles X. of Sweden until the peace of Oliva (166o). A war against Turkey was brought to a close by the victory of the imperialist general Montecuccoli at St. Gotthard, followed by a twenty years' truce with the sultan. The first war with France (1672-78) was concluded by the treaty of Nijmwegen (1679). The empire was again in a state of war with France in 1682-84, and in 1689 Leopold joined the Grand Alliance against Louis XIV. (See GRAND ALLIANCE, WAR OF THE.) Peace was concluded at Ryswick in 1697, though Leopold did not come to terms until some months later. After four years of peace the empire was involved in the war of the Spanish Suc cession (q.v.). The early course of the war was not favourable to the imperialists, but the tide turned with the great victory of Blenheim before Leopold died on May 5, 1705.
During this reign some important changes were made in the con stitution of the Empire. In 1663 the imperial diet entered upon the last stage of its existence, and became a body permanently in session at Regensburg; in 1692 the duke of Hanover was raised to the rank of an elector, becoming the ninth member of the electoral college; and in 1700 Leopold greatly in need of help for the impending war with France, granted the title of king of Prussia to the elector of Brandenburg. The net result of these and similar changes was to weaken the authority of the emperor over the members of the Empire, and to compel him to rely more and more upon his position as ruler of the Austrian archduchies and of Hungary and Bohemia, and Leopold was the first who really appears to have realized this altered state of affairs and to have acted in accordance therewith.
Leopold's letters to Marco d'Aviano from 1680 to 1699 were edited by 0. Klopp and published at Graz in 1888. Other letters are found in the Fontes rerum Austriacarum, Bande 56 and 57 (Vienna. 1903-04). See also F. Krones, Handbuch der Geschichte Osterreichs (1876-79) ; R. Baumstark, Kaiser Leopold I. (1873) ; A. F. Pribram, Zur Wahl Leopolds I. (Vienna, 1888) ; K. T. von Heigel, Neue Beitreige zur Cha rakteristik Leopolds I. (1890).